The invention relates to a sheet-guiding device for a sheet-fed printing machine, more particularly, including an impression cylinder and a further cylinder adjacent thereto, the sheet-guiding device having a sheet-guiding element arranged for guiding a sheet transported by the impression cylinder when the further cylinder is set off or disengaged from the impression cylinder.
The published German Patent Document DE 431 87 77 C2 describes such a sheet-guiding device, which includes two blast-air tubes of which one is arranged in a wedge-shaped space upline of the printing zone, and the other is arranged in a wedge-shaped space downline of the printing zone of a printing unit that is not involved in printing. Although blast-air tubes arranged outside the printing zone and separately from a blanket cylinder can possibly be used to prevent thin paper sheets from striking the blanket cylinder not included in the in-line process in the region of the printing zone, this cannot be assured for pasteboard or cardboard sheets which are to be processed. There is therefore the risk that the board sheets, because of the stiffness thereof, cannot be kept at a distance from the blanket cylinder by the blast-air tubes in the region of the printing zone and will strike the blanket cylinder, due to which the fresh printed image on the sheets is smeared.
In the German Patent 197 19 624, a further sheet-guiding device is described which corresponds to the generic type thereof mentioned at the introduction hereto and wherein a sheet-guiding element is provided in the cylinder gap of a rubber blanket cylinder or varnishing blanket cylinder and covers the printing zone, as is shown in the drawings of the German patent. In an embodiment of the sheet-guiding element realized as a guide plate or tongue, although the rear or trailing edge of the sheet is able to slide along the sheet-guiding element without damaging the imprint or overprint when stiff sheets of board are being printed, sufficient free space is required in order to integrate the sheet-guiding element into the cylinder gap. The free space is generally not available, because the blanket clamping devices, which are arranged in the cylinder gap, themselves take up a great deal of space. For this reason, retrofitting of the sheet-guiding element to printing machines which are already in use is not possible.
In the published German Patent Document DE 196 03 666 C2, there is further described, as prior art, a safety guard device having a guard member which is pivotable into an interspace between a plate cylinder and a transfer cylinder in order to ensure effective protection during a non-stop printing-plate exchange. The safety guard device is provided for a web-fed printing machine, and the interspace is not located in the region of a printing zone of an impression cylinder.
Accordingly, it is an object of the invention to provide a sheet-guiding device by which trouble-free passage of freshly printed or varnished sheets of cardboard or pasteboard through a unit not directly involved in the in-line process is ensured.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a sheet-guiding device with a sheet-guiding element for a sheet-fed printing machine having an impression cylinder and a further cylinder adjacent thereto, the sheet-guiding element being disposed for guiding a sheet transported by the impression cylinder when the further cylinder is set-off from the impression cylinder, the further cylinder comprising a cylinder selected from the group thereof consisting of an applicator cylinder for applying one of ink and varnish, respectively, to a sheet lying on the impression cylinder, and a tool cylinder for applying a finishing step to a sheet lying on the impression cylinder, the sheet-guiding element being disposed separately from the further cylinder and covering an impression zone of the impression cylinder.
In accordance with another feature of the invention, the sheet-guiding element has at least one of a sheet-sliding and a blower nozzle face directed towards the impression cylinder, the face extending over the impression zone, at least approximately concentrically with the peripheral surface of the impression cylinder.
In accordance with a further feature of the invention, the sheet-guiding element has at least one of a sheet-sliding and a blower nozzle face directed towards the impression cylinder, the face extending over the impression zone, at least approximately parallel to a tangential line extending to the impression cylinder through the impression zone.
In accordance with an added feature of the invention, the sheet-guiding element extends through a nip formed in the region of the impression zone between the impression cylinder and the further cylinder.
In accordance with an additional feature of the invention, the nip has a nip width determined by a position of the further cylinder wherein it is withdrawn from the impression cylinder, and wherein a drive gear of the impression cylinder and a drive gear of the further cylinder are out of meshing engagement with one another.
In accordance with yet another feature of the invention, the nip has a nip width enlarged by an alignment therewith of a cylinder gap of the further cylinder facing towards the rotating impression cylinder, and including a security device for securing the further cylinder against rotation out of the aligned rotary position thereof.
In accordance with yet a further feature of the invention, the impression cylinder and the further cylinder are formed with respective peripheral circular arcs having a minimum spacing therebetween which is less than one tenth of a meter.
In accordance with an alternative feature of the invention, the impression cylinder and the further cylinder are formed with respective peripheral circular arcs having a minimum spacing therebetween which is less than one centimeter.
In accordance with yet an added feature of the invention, the sheet-guiding device includes a mounting for mounting the sheet-guiding element so that the sheet-guiding element is movable into the nip.
In accordance with yet an additional feature of the invention, the mounting is constructed so that the sheet-guiding element is insertable into the nip at least approximately tangentially to the impression cylinder.
In accordance with still another feature of the invention, the mounting is-constructed so that the sheet-guiding element is pivotable into the nip at least approximately coaxially with the impression cylinder.
In accordance with another alternative feature of the invention, the mounting is constructed so that the sheet guide element is pivotable into the nip at least approximately coaxially with the further cylinder.
In accordance with still a further feature of the invention, the sheet-guiding device includes a remotely controllable actuator connected to the sheet-guiding element for displacing the sheet-guiding element into and out of the nip.
In accordance with still an added feature of the invention, the actuator is connected to the further cylinder for displacing the further cylinder into a position wherein it is withdrawn from the impression cylinder.
In accordance with a concomitant aspect of the invention, there is provided a sheet-fed printing machine having a sheet-guiding device constructed with at least one of the foregoing features.
Thus, the further cylinder cooperating with the impression cylinder and serving as the applicator cylinder can be a blanket cylinder or a varnishing blanket cylinder or a printing-form or varnishing-form cylinder and, when serving as the tool cylinder, can be a stamping, embossing, creasing or perforating cylinder. The impression zone extends axially parallel on the peripheral surface of the impression cylinder.
The impression zone is normally also referred to as the printing zone or line if the impression zone is formed with the applicator cylinder. An impression zone formed with the tool cylinder can be referred to as the contact zone or line, within the area of which the processing of the sheet located between the cylinders takes place. The sheet-guiding element is not applied to the further cylinder, as is provided in the aforementioned published German Patent Document DE 197 19 624 C1, but rather, in contrast with the latter, is applied separately from the further cylinder so that it can move on the sheet-fed printing machine and, for example, on the frame of the latter. As viewed in the radial direction of the impression cylinder, the sheet-guiding element is located directly above the impression zone thereof, so that the sheet conveyed through the inactive printing, varnishing or processing unit cannot strike the further cylinder with a sheet trailing edge within the region that is critical due to the proximity of the further cylinder to the impression cylinder, because the sheet-guiding element is located between the further cylinder and the sheet. Acting as a spacer, this prevents the sheet from coming into contact with the further cylinder during the passage thereof through the inactive unit.
Assurance is therefore always provided that the ink (varnish) previously applied to the sheet in at least one printing unit (varnishing unit) disposed upline of the inactive unit in the in-line process does not come into contact with the further cylinder and, therefore, not smeared thereby.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet-guiding device for a sheet-fed printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: